Piston rod joint

ABSTRACT

A joint for connecting a crosshead extension rod to a piston rod end-to-end. The piston rod has an integral tapered threaded pin at its end, a straight threaded portion inwardly of the pin, and an undercut section between the pin and the straight threads. The extension rod has a tapered threaded bore receiving the pin. A lock nut is engaged with the straight threads and tightened against the end face of the extension rod to maintain the undercut section under tension throughout the working cycle.

United States Patent [151i 3,704,904 Rizzone 511 Dec. 5, 1972 [s41PISTON ROD JOINT 2,045,520 6/1936 Davison ..287/l25 Inventor: Michael L.Rizzone Dallas, Tex. 2,510,377 6/1950 Carr "92/165 [7 3] Assignee:United States Steel Corporation 2 Primary ExaminerAndrew V. Kundrat [22]Filed: Jan. 24, 1972 Attorney-Walter P. Wood [21] App]. No.: 220,122[57] ABSTRACT a A joint for connecting a crosshead extension rod to a[52] US. Cl. ..2s7/12s Piston rod The Piston rod has an integral [51]Int. Cl ..F16d 1/00 tapered threaded P at its end, a straight threaded[53] Field of Search ..2s7/125, 117, 128; 285/333, Portion inwardly ofthe P and an undercut Section 5 5 279/99,)0 between the pin and thestraight threads. The extension rod has a tapered threaded borereceiving the pin. [56] References cited A lock nut is engaged with thestraight threads and s tightened againstthe end face of the extensionrod to UNITED STATES PATENTS maintain the undercut section under tensionv throughout the working cycle. 1,378,290 5/l92l Smith ..279/l001,879,856 3 Claims, 2 Drawing Figures 9/1932 Peterson "287/125PAIENIEDUEC SIQTZ FIG. 2.

PISTON ROD JOINT This invention relates to an improved jointparticularly for connecting a crosshead extension rod to the piston rodof a pump. I

A conventional slurry pump or mud pump has a piston rod to which isjoined an extension rod leading a crosshead. At this joint the pistonrod is threaded into a bore in the end of the extension rod. Thejointtends to fail through fatigue at the thread root of the piston rodwhich lies in the plane of the end face of the extension rod.

An object of the present invention is to provide an improved joint whichforestalls failure of a piston rod at the foregoing location.

A further object is to providea piston rod joint in which the piston rodhas an undercut section prestressed under tension where it enters thebore in the extension rod, thereby forestalling failure at thislocation.

In the drawing:

FIG. 1 is a side elevational view, with parts broken away, of a pump inwhich the joint of the present invention is embodied; and

FIG. 2 is a vertical sectional view on a larger scale of the joint.

FIG. 1 shows a reciprocating pump which has a piston rod 12, and anextension rod 13 joined end-toend with the piston rod. The joint betweenthe piston rod and the extension rod is constructed in accordance withmy invention, but otherwise the pump may be of conventional constructionand hence is not shown in detail. The extension rod leads to a crosshead(not shown) which is connected to a suitable drive.

As best shown in FIG. 2, the end face of the extension rod 13 has atapered threaded bore 16. The piston rod 12 has an integral taperedthreaded pin 17 at its end, a straight threaded portion 18 inwardly ofthe pin, and an undercut section or groove portion 19 between the pinand the straight threads. Preferably the end face of the piston rod hasa socket 20. The tapered pin is threadedly engaged with the threads ofbore 16. A lock nut 21 is threadedly engaged with the straight threadedportion 18 of the piston rod-12 and has a flange 22 which abuts theannular end face of the extension rod 13. Flange 22 clears the undercutsection 19.

The tapered threaded connection of pin 17 affords maximum tightness,while the socket 20 makes the pin limber and distributes the thread loadalong the length of the pin element-to-element. In the absence of thesocket, the extension rod 13 at the joint is under compression and thepin 17 under tension. I tighten nut 21 sufficiently to prestress theundercut section 19 under a tensile load greater than the working loadof the pump. Consequently the undercut section remains under tensionthroughout the pumping cycle.

The critical portion of a conventional joint, where failure is mostlikely to occur, is in a thread root of the piston rodopposite the endface of theextension rod.

My invention eliminates any thread root at this location, andprovidesinstead an undercut stress-relieved section which. always remains undertension. Consequently there is no alternating tensile and compressiveloading such as leads to fatigue failure.

Iclaim:

l. The combination, with a piston rod and an extension rod connected tosaid piston rod end-to-end, of an improved oint comprising an integraltapered threaded pin at the end of said piston rod, a straight threadedportion on said piston rod inwardly of said pin, an undercut grooveportion on said piston rod extending between the pin and the straightthreads, said extension rod having a tapered threaded bore in its endface receiving said pin, and a lock nut threadedly engaging saidstraight threaded portion and abutting the end face of said extensionrod, the end face of said extension rod being opposite said grooveportion, said lock nut clearing said groove portion and being tightenedsufficiently to maintain said groove portion under tension within theworking load on the joint.

2. A combination as defined in claim 1 in which said pin has a socket inits end face.

3. A combination as defined in claim 1 in which said piston rod isembodied in a reciprocating pump.

1. The combination, with a piston rod and an extension rod connected tosaid piston rod end-to-end, of an improved joint comprising an integraltapered threaded pin at the end of said piston rod, a straight threadedportion on said piston rod inwardly of said pin, an undercut grooveportion on said piston rod extending between the pin and the straightthreads, said extension rod having a tapered threaded bore in its endface receiving said pin, and a lock nut threadedly engaging saidstraight threaded portion and abutting the end face of said extensionrod, the end face of said extension rod being opposite said grooveportion, said lock nut clearing said groove portion and being tightenedsufficiently to maintain said groove portion under tension within theworking load on the joint.
 2. A combination as defined in claim 1 inwhich said pin has a socket in its end face.
 3. A combination as definedin claim 1 in which said piston rod is embodied in a reciprocating pump.